There have been countless movies with great depictions of drug trips (Scorsese's The Wolf of Wall Street featuring a recent masterpiece of the genre) but relatively few that focus entirely on them.

Fear and Loathing in Las Vegas, which was released 20 years ago tomorrow, stands alone as a celebration and commiseration of the multifarious drug binge, a 118-minute start-to-finish odyssey into drugs and how they can be fun, frightening and futile. A critical and financial failure (at least at the time, it is remembered more fondly now and has since attained cult status), it delights in its simple mission, a sharply-focused look at an experiential blur.

Director Terry Gilliam once described the narrative thus:

"We start out at full speed and it's WOOOO! The drug kicks in and you're on speed! Whoah! You get the buzz – it's crazy, it's outrageous, the carpet's moving and everybody's laughing and having a great time. But then, ever so slowly, the walls start closing in and it's like you're never going to get out of this fucking place. It's an ugly nightmare and there's no escape."

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When principal photography started, there was no firm budget in place and the production was subject to "all sorts of chaos", according to Gilliam, operating as though "one leg was shorter than the other." Casinos were more strict on filming than expected, only seven or eight animatronic reptiles turned up instead of the 25 ordered, and budget constraints meant that returning Vegas to the 1970s period required rear-projecting footage from an old ABC television show called Vega$ behind the actors. At one point, the crew ran out of time and had to shoot a day scene in the desert at night ("There were some dailies of that footage that were really funny; sometimes the takes would go on a bit too long, and the special effects guys would cut off the Fuller's Earth [dust used to diffuse light], causing the scene to suddenly go from full sun to complete blackness!").

But, in spite of the uneven production, last-minute script re-writes and a litany of quibbles from the studio, Gilliam managed to get off the ground what Martin Scorsese and Oliver Stone had failed to before him, an unapologetic film adaptation of Hunter S. Thompson's mind-bending book.

Credit for the ramshackle operation also goes to Johnny Depp, who went above and beyond with his preparation, moving into the basement at Thompson's ranch in order to study his habits and mannerisms. Depp went through the author's notebook from the real-life trip Fear and Loathing in Las Vegas was based on ("Not only is [the book] true, but there's more and it was worse," Depp said), drove around town in his infamous fireapple red Chevrolet Caprice convertible known as 'The Great Red Shark', and had Thompson shave his head in line with the writer's male pattern baldness. It seems Thompson was all in too; many of the costume elements and props used in the film actually belonged to him.

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If Depp's performance was one pillar on which the film would live or die, the other would be the cinematic quality of the chemical indulgences. Here, director of photography Nicola Pecorini avoided the common trap of going too surreal. There were no montages of flying around the galaxy on a unicorn, however aesthetically tempting that might be, the trips instead being characterised by - as they are in real life - corruptions of and in reality. Raoul Duke and Dr. Gonzo's descent into mania was fundamentally rooted in Las Vegas, it was visuals and perceptions that were twisted more than the environment itself, and the film crucially gave us as many opportunities to voyeuristically gawp at the duo from the outside and consider how banal trips appear for those not on them, as it did to lock us in the minds of those afflicted.

That said, there were still many bizarre visuals that harnessed lighting, camera control, CGI, animatronics and countless other elements, and that's not to mention the erratic editing.

Here are five of the drugs taken in the film, their most notable effects, and how Pecorini briefly outlined the cinematic qualities of each to American Cinematographer in May 1998 (we've reached out to Pecorini for some elaboration):

Diethyl ether

(Similar effects to those of alcohol but more potent - distorted thinking, euphoria, visual/auditory hallucinations at higher doses)

"Loose depth of field; everything becomes non-defined"

Adrenochrome

(Thought disorder, derealisation, euphoria)

"Everything gets narrow and claustrophobic, move closer with lens"

Mescaline

(Similar to those of LSD and psilocybin but with an emphasis on intense colour perception. Visual patterns, synesthesia, an altered sense of time and self, and, uniquely to mescaline, a 'geometricisation'/cubism of three-dimensional objects, may be experienced)

"Colours melt into each other, flares with no sources, play with colour temperatures"

Amyl nitrite

(Head rush, dizziness, muscle relaxation, sensation of heat)

"Perception of light gets very uneven, light levels increase and decrease during the shots"

LSD

(Hallucinations, mood heightening, speeding up or slowing down of time and movements, distortion of colour, sound and objects)