Horror, Sleaze and Trash.

Before starting abusing drugs in 1971, he mostly took medication to treat his known ailments, even though it is also known he was already using prescription drugs like Darvon for migraines. Even then, he often took more than the recommended dosage.

His known medication before 1971 was Insulin for his diabetes (diagnosed in 1954, along with high blood pressure), and Nitroglycerin for his heart.

Sometime around 1971, he started to heavily abuse drugs like Amphetamines, Quaaludes, and later liquid Valium and Morphine, Pentorbarbital, Percodan, Oxycodone, …That same year he also started wearing sunglasses at times, his drugs use being one of the reasons.
He often mixed his pills with alcohol, generally Vodka, Whiskey or Cognac, an habit he kept up until the end in Jonestown.

There are reports he was using cocaine and heroin at some point, but there are no other details about it, beside the testimony of Neva Sly Hargrave and Tim Carter (who mentioned only Heroin).
The drug he certainly abused the most though was Amphetamines (not to be confused with Methamphetamine). He took it to stay awake, often working 20-hour days or even more, and get up in the morning. His known paranoia was then fueled even more by the drug intake. People in the congregation had no idea of his addiction and the majority thought the short and long time side effects of the drug were due to some chronic illness. Among the side effects he experienced : quicker reaction time, feeling of energy, chronic trouble sleeping, dry mouth, headache, hostility, severe anxiety, increased heart rate, hypertension, paranoia, violent behavior, convulsions, loss of coordination, obsessive behavior.

A side effect he did not seem to experience with Amphetamine abuse was loss of appetite. Amphetamines can be used as appetite suppressants and in diet pills, but he often talked about food and how he had to try to resist it. In 1972 he made a few references to fasting to lose some weight quickly, and in 1974, he said he can get into a “food problem” because it keeps his mind from thinking. Food  was mentioned by Stephan as another addiction for his father, just like drugs.
Quaaludes and Pentorbarbital were used to sleep at night. If he doubled the dosage of Amphetamine, he actually tripled the recommended dosage to sleep. At high doses Pentorbarbital can cause mental confusion, irritability, paranoid or suicidal ideation and impair judgment, and coordination.

Once in Jonestown he relied more and more on Valium for his anxiety. In February 1978, he was prescribed antibiotics for his cough (which later resulted in a lung infection),Terramycin, Erythromycin and Ampicillin. As with all medications, he also abused them, and natural defenses can be affected by their excessive use. Around September 1978, he started using Elavil and Placidyl for depression, both by injection.