KIAMBU, Kenya, Oct 7 (Reuters) - In a discreet clinic just outside the Kenyan capital, a recovering heroin addict named Peter holds the hand of his two-year-old daughter as he drinks a dose of methadone.

Peter’s teeth are yellow and he looks much older than 26.

“I miss nothing and wish I could totally forget it,” he says of the 14 years he was addicted to heroin. Taking the treatment means his wife has given him a second chance.

Kenya is seeing more and more addicts. The number of people injecting drugs jumped by more than 50% in the past eight years and the majority of users inject heroin, the health ministry says.

A single heroin dose costs about 150 Kenyan shillings ($1.45), former users told Reuters, roughly a fifth the average price of a single dose in the United States, according to the United Nations.

Young people are using across all social classes, said David Ndegwa, health director in Kiambu County, where Medecins Sans Frontieres (MSF) opened a clinic this month 20 km (12 miles) north of the capital.

“They are the most productive members of our society,” Ndegwa said.

Heroin enters the East African nation at Mombasa, a port city that is a growing hub for drugs from Afghanistan bound for the West, he said.

Africa had the world’s fastest growing number of heroin users from 2006 to 2016, according to the U.N. Office on Drugs and Crime.

The MSF clinic is the first in Kenya to offer heroin users methadone treatment and all other necessary free services.

When they arrive for their methadone - given in a plastic cup instead of an injection - users can also get psychological counselling, care for diseases such as HIV/AIDs, tuberculosis and hepatitis, clean drinking water and treatment for infected needle wounds.

Previously, patients used to have to go to different clinics for each treatment.

“Care was fragmented,” said Angela Thiong’o, MSF’s drug use activity manager in Kenya. “This is a one-stop shop.”

Methadone attaches to the brain’s opioid receptors, eliminating cravings and withdrawal symptoms. The accepted practice is to give heroin users methadone, with no deadline for weaning them off, experts say.

Jason, 26, started using methadone on Feb. 28, 2018, after five years of heroin use landed him in jail, made him sick and resulted in fights with his parents.

He takes his daily dose at the MSF clinic because it is close to home and he can spend time with recovering addicts.

Now, he and his friend, Edwin, try to talk users into treatment at heroin dens with names such as Nigeria, Columbia and Gaza, where they used to buy their daily hits.

“I want them to get out of the den and be someone who is recognised by society,” Jason said. (Reporting by Maggie Fick Editing by Karishma Singh and Robert Birsel)