Bryn Lennon / Getty Images Lance Armstrong in action on stage 18 of the 2009 Tour de Franc in Annecy, France, July 23, 2009.

“Enough is enough.” With those loaded words, seven-time Tour de France winner, cancer survivor, and patient advocate Lance Armstrong put an end to the accusations of doping that have dogged him for years. Faced with a deadline for responding to allegations by the U.S. Anti-Doping Agency (USADA) that he both used and distributed performance enhancing drugs during his competitive cycling career, Armstrong decided on Thursday to avoid arbitration with USADA and accept the agency’s punishment.

USADA swiftly revoked all seven of Armstrong’s Tour titles and banned him for life from the sport of cycling. The international cycling federation, Union Cycliste Internationale, has yet to take action, demanding an explanation from USADA for the agency’s censure.

Armstrong has been a controversial figure in a sport buffeted by doping scandals; as the only cyclist to win the grueling Tour de France seven times, he became a lightning rod for rumors and accusations of cheating through doping. Armstrong won the first of his consecutive Tour titles three years after being diagnosed with testicular cancer.

USADA says it has evidence [PDF] that Armstrong had since 1999 led a conspiracy involving trainers and lab officials to encourage doping among certain cycling teams, as well as to cover up allegedly positive results from some riders. Two former members of Armstrong’s United States Postal Service (USPS) and Discovery Channel teams — Floyd Landis and Tyler Hamilton — confessed to doping and told the agency they knew Armstrong used banned substances to fuel several of his Tour victories between 1999 and 2005.

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In a statement posted on his website, Armstrong detailed his reasons for ending his fight against USADA, saying that the strain of the constant accusations has “taken a toll on my family, and my work for our foundation and on me.” He maintains his innocence. “I refuse to participate in a process that is so one-sided and unfair,” he wrote of the anti-doping agency’s investigation. “There is zero physical evidence to support [the] outlandish and heinous claims. The only physical evidence here is the hundreds of controls I have passed with flying colors.”

By choosing not to arbitrate, the testimony and evidence that USADA has against Armstrong may never be heard, leaving unanswered the relevant question: Did he or didn’t he take illegal performance enhancing drugs during his competitive career?

We may never know the answer to that, but what follows are drugs USADA has accused him of taking (below, is the abridged rundown taken from the agency’s official charges [PDF]). USADA’s allegations are based on testimony the agency took from eyewitnesses — members of Armstrong’s USPS and Discovery Channel cycling teams who say they saw Armstrong taking the drugs or in possession of them, or were in some cases allegedly given the banned performance enhancers by Armstrong or doctors working with the teams:

Erythropoietin (EPO), also known as “E,” “Po,” “Edgar” or “Edgar Allen Poe,” among other names. EPO is used by athletes to increase the number of red blood cells in their circulatory system which are available to carry oxygen. … Even after the EPO urine test was developed and implemented in sport in late 2000 EPO was difficult to detect and the Respondents [Armstrong, a team director, team captain and team doctors] implemented a number of means to avoid detection of EPO use, including: micro-dosing (i.e., using smaller amounts of EPO to reduce the clearance time of the drug), intravenous injections (i.e., injecting the drug directly into the vein rather than subcutaneously to reduce clearance time), saline, plasma or glycerol infusions (described below) and various effort to avoid testing by drug testers at times that EPO might still be detectable in the riders’ urine. … Multiple riders with firsthand knowledge will testify that between 1998 and 2005 Armstrong personally used EPO and on multiple occasions distributed EPO to other riders. Blood transfusions (a/k/a “blood doping”). Blood transfusions generally involve the extraction of an athlete’s own blood pre-competition and re-infusion of that blood shortly before or during competition (e.g., in the evening or on a rest day in a multistage race) to increase the athlete’s oxygen carrying red blood cells. By increasing the number of circulating red blood cells, transfusions increase the oxygen carrying capacity of the blood and enhance endurance and recovery. No effective anti-doping test has yet been implemented to detect autologous transfusions (i.e., transfusions of an athlete’s own blood). … Multiple riders will testify that during the period 2000-2005 Armstrong used blood transfusions, was observed having blood re-infused, including during the Tour de France, and had blood doping equipment at his residence. Testosterone. Also known on the USPS and Discovery Channel cycling teams as “oil.” Testosterone is an anabolic agent and can increase muscle mass and strength. In smaller doses anabolic agents such as testosterone can promote muscle recovery from strenuous exercise and increase endurance. Andriol consists of testosterone undecanoate, a steroid which can be mixed with oil and taken orally. Taken in this way the drug can be absorbed into the lymphatic system without being transported to the liver, making the drug more effective and reducing the prospect of liver damage. Multiple riders who competed on the USPS and Discovery Channel teams from 1998 through 2007 have reported that Dr. Ferrari [an alleged co-conspirator] developed a method of mixing testosterone (i.e., andriol) with olive oil for oral administration. … USADA has eyewitness statements from multiple sources that Lance Armstrong used testosterone and administered the testosterone-olive oil mixture to himself and other riders. Human Growth Hormone (hGH). Human growth hormone is improperly used in sport to increase strength and lean muscle mass, to assist in weight loss and promote recovery. Multiple riders who competed on the USPS and Discovery Channel teams from 1998 through 2007 have reported to USADA that team director Johan Bruyneel, team trainer Jose Pepe Marti and team doctors Luis del Moral and Pedro Celaya provided human growth hormone to team members. Corticosteroids (e.g., cortisone). These drugs reduce inflammation, assist in recovery and can provide a burst of energy and create a temporary feeling of increased energy and well-being. Throughout the relevant time period, corticosteroids were improperly provided to cyclists by team doctors and trainers to increase energy and enhance performance. … USADA will also rely upon firsthand testimony from witnesses who were aware of Armstrong’s use of cortisone without medical authorization. Saline and plasma infusions. Throughout much of the relevant period the UCI [Union Cycliste International] employed a blood monitoring program and would not permit riders to compete if the rider’s hematocrit (i.e., percentage of mature red blood cells) exceeded 50%. To avoid exceeding the 50% hematocrit threshold and to prevent detection of the rider’s EPO use and/or blood transfusions, Respondents used the prohibited technique of saline, plasma or glycerol infusions to mask their use of prohibited substances and/or methods. … USADA will also present testimony concerning infusions given to numbers USPS riders, including Lance Armstrong.

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In a statement issued in response to Armstrong’s decision on Friday, USADA CEO Travis Tygart said, “Nobody wins when an athlete decides to cheat with dangerous performance enhancing drugs, but clean athletes at every level expect those of us here on their behalf, to pursue the truth to ensure the win-at-all-cost culture does not permanently overtake fair, honest competition. Any time we have overwhelming proof of doping, our mandate is to initiate the case through the process and see it to conclusion as was done in this case.”

In outlining the allegations against Armstrong, USADA said it based its punishment on the following:

The anti-doping rule violations for which Mr. Armstrong is being sanctioned are: (1) Use and/or attempted use of prohibited substances and/or methods including EPO, blood transfusions, testosterone, corticosteroids and masking agents. (2) Possession of prohibited substances and/or methods including EPO, blood transfusions and related equipment (such as needles, blood bags, storage containers and other transfusion equipment and blood parameters measuring devices), testosterone, corticosteroids and masking agents. (3) Trafficking of EPO, testosterone and corticosteroids. (4) Administration and/or attempted administration to others of EPO, testosterone and cortisone. (5) Assisting, encouraging, aiding, abetting, covering up and other complicity involving one or more anti-doping rule violations and/or attempted anti-doping rule violations.

In following the World Anti-Doping Agency regulations for testing of athletes, USADA can test athletes during competitions and any time afterward, without notice. The samples are kept for eight years, and the agency can re-test samples as screening technology for detecting banned substances, or new performance-enhancing drugs, improves. “The out-of-competition situation where athletes don’t know if I will come knocking on their door wanting a urine or blood sample is a fantastic deterrent,” says Anthony Butch, director of the UCLA Olympic Analytical Laboratory that tests samples from Olympic athletes for the World Anti-Doping Agency, the U.S. Olympic Committee and the National Football League and Minor League Baseball.

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While the surprise element can help catch doping athletes before they’ve had time to clear their system of banned substances, Butch says that’s not the only way testers are going after cheaters. New tests have been developed to detect illegal concentrations of performance enhancers much more accurately as well. Human growth hormone and testosterone, for example, pose particular challenges for testers, since they occur naturally in the body to varying degrees — so, where is the line between normal and performance enhancing?

In testing for hGH, technicians rely on a sophisticated understanding of how the body reacts when you inject higher concentrations of the hormone — other forms of the hormone start to drop. So, testers look at the ratio between hGH and these other derivatives to detect foul play. Too large a gap between these concentrations is a red flag that the user may be boosting with injected hGH. To further improve their chances of detecting doped levels of the hormone, Butch says it may soon be possible to look for the molecular fingerprint that hGH leaves on other compounds, even after the actual hormone has long been cleared from the body. “We can go from a 36-hour window for detecting hGH to a couple of weeks,” he says.

And while you could argue that the line between legitimate performance enhancement — which is, after all, what training is all about — and doping is a fine one, Butch says it’s helpful to remember one thing about the banned substances. “A lot of the things on the [banned] list are on there because they are harmful,” he says. “They have health consequences. And when people are young, they think they are invincible, and that these things won’t have adverse effects on them. But they’re completely wrong.”