Addiction

A major theme in the show is drug addictions. Most of the characters in the show have had an addiction, and each member of the gang is an alcoholic. (The Gang Gets Quarantined)

Complete List of Drugs
Meth is mentioned in certain episodes, but isn't used.
 * Glue, Spray Paint, Poppers, Nitrous Oxide, Gasoline (inhalants)
 * Marijuana, Hashish (cannabis)
 * Crack / Cocaine
 * Oxycodone (and pharmaceuticals)
 * Alcohol (depressants)
 * Steroids
 * LSD
 * Heroin (dealt only)
 * Angel Dust (PCP)
 * Cigarettes
 * Ecstasy
 * Bath salts (not ingested by the gang)
 * Amphetamines were likely the drug referred to as Rita-rall (likely a crushed combination of Ritalin and Adderall) that Frank Reynolds and Dennis were snorting in The Gang Reignites The Rivalry.

Ryan McPoyle is seen inhaling Pledge in a couple of episodes, and he asks Mac and Dennis, "Where do you keep your pledge?" while in The Bar before being shooed away. (Charlie Goes America All Over Everybody's Ass)

Charlie
has been addicted to huffing glue since he was a child. During he and Mac huffed glue in his mom's basement. Charlie huffs glue to help him sleep at night as well. It is a part of his cat food, beer, and glue combination that allows him to sleep through the cats at his apartment. Charlie also states that glue overdoses are common in his life. Sometimes Charlie huffs non-toxic glue by accident. (A Very Sunny Christmas, Underage Drinking: A National Concern, Dennis Reynolds: An Erotic Life)

Although Charlie prefers glue he is also known to use other inhalants, such as spray paint and poppers. (Sweet Dee's Dating a Retarded Person)

Charlie was also addicted to cocaine while trying to sell it on the streets of Philly. (The Gang Gets Whacked (Part 2))

He has also had a minor addiction to Dee's steroids while training to be a streetfighter. (Hundred Dollar Baby)

Charlie, Dee, Dennis and Frank smoke weed with Country Mac. (Mac Day)

Frank puts a bunch of sedatives in a brownie which Charlie eats. (The Gang Dances Their Asses Off)

Frank puts LSD in Charlie's beer while they are tailgating a football bootcamp. (The Gang Gets Invincible)

Charlie briefly took up smoking to deal with the stress of the mailroom job, and later admits to smoking in secret with Dee. (Sweet Dee Has A Heart Attack, Hero or Hate Crime?)

Dee
smoked crack while trying to fail a drug test, but quickly became addicted. (Dennis and Dee Go on Welfare)

When training to improve her fighting skills Dee becomes addicted to steroids. She is shown going through several bottles of the pills during a montage of only a few days. (Hundred Dollar Baby)

Along with Charlie, Dee became addicted to cocaine, despite them rubbing on the gums to avoid addiction. (The Gang Gets Whacked (Part 2))

Dee, Charlie, Dennis and Frank smoke weed with Country Mac. (Mac Day)

Dee smokes cigarettes when she's in a rut. She also buys cigarettes with the money Dennis gives her for a tip to the cashier, and is later revealed to be smoking them in secret with Charlie. (The Gang Broke Dee, Hero or Hate Crime?)

Dee used prescription stimulants "uppers" to stay awake while drunk (the gang beats Boggs)

Frank
Frank Reynolds became addicted to anti-anxiety medications due to not wanting to sift through duds. He spent time in a mental hospital due to the prolonged effects resulting from taking too many pills. (Sweet Dee Has a Heart Attack)

Frank was given an intervention by the gang because of his constant marijuana use, and alcohol abuse. Frank smoked marijuana from a water bong (Sweet Dee Has a Heart Attack) and in joints. The fact that the he has gone too far even for them is an exceptional feat.

Frank, Dee, Charlie and Dennis smoke weed with Country Mac (Mac Day)

Frank snorts Rita-rall in (The Gang Reignites the Rivalry)

Frank snorts cocaine in (Dee Gives Birth)

Frank snorts a lot of cocaine (Frank's Brother) He admits that he snorts coke every day as part of his "morning routine. (Wolf Cola: A Public Relations Nightmare).

Dennis
along with Dee buys and becomes addicted to crack. (Dennis and Dee Go on Welfare)

and both try ecstasy while trying to gain fame in Frank Sets Sweet Dee on Fire. Dennis begins living a party lifestyle, going out clubbing every night and taking ecstasy with the group of women who "can make you or break you" in Philadelphia.

Dennis, Frank, Dee and Charlie smoke weed with Country Mac (Mac Day)

Dennis smoke cigarettes regularly in the first couple seasons of the show, and his blowing smoke directly into Charlie’s face in “Charlie Goes America All Over Everyone’s Ass” is the catalyst for Charlies arc during the episode.

Other Characters
Rickety Cricket develops a cocaine addiction while selling the drugs to other homeless people for Dee and Charlie. This addiction partly contributes to his legs being broken. (The Gang Gets Whacked (Part 2)

Artemis mentions that she smokes hashish. (Charlie Goes America All Over Everybody's Ass)

Artemis mentions she is "insanely high on mescaline" at a Halloween party.

The Waitress has had a long time problem with alcohol, and on occasion, drugs. She seems to be sober most of the time, and voluntarily attends AA (The Gang Gives Back). In later seasons, she tends to relapse when emotionally stressed or depressed (The Gang Goes to the Jersey Shore), anxious (The High School Reunion, Part 2: The Gang's Revenge), or angry (Who Pooped the Bed?), and often her relapses coincide with interactions with the gang. She has relapsed on drugs as well as alcohol, such as when she does ecstasy in (The Gang Goes to the Jersey Shore, when she's "really off the wagon: drinking, drugs..."

Artemis smokes weed (Frank's Little Beauties)

Bill Ponderosa snorts cocaine (The Gang Squashes Their Beefs)

Gail the Snail smokes weed (The Gang Gives Frank an Intervention)

Alcoholism
Every member of the Gang is an alcoholic as well as The Waitress, and Bonnie Kelly.

When the Gang quarantines themselves to avoid a flu epidemic sweeping through Philadelphia, they start experiencing symptoms that they think are the flu anyway. They drink some booze that Charlie had hidden (in bleach bottles, because where else would you put it) and notice they feel better right away, which makes them realize that the "flu" they had was actually alcohol withdrawal, because they had refrained from drinking as part of the quarantine and to keep themselves from getting the flu. (The Gang Gets Quarantined)

Charlie and the Waitress have both been involved in the Alcoholics Anonymous program. (The Gang Gives Back)

Charlie, Mac, Dennis, Dee and Frank are all severe alcoholics, though Frank drinks the least out of the gang he is still a alcoholic and we see him drunk more than anyone on the show.

Other Drug Use
Frank, Charlie and Dennis each take acid during episodes of the show, but no addiction is shown to have come from this. (The Gang Gets Invincible, The Gang Finds a Dumpster Baby)

Mac huffs glue with Charlie but is never mentioned or shown having an addiction to it. Mac also joins Charlie inhaling poppers in order to overcome the effects of his concussion. (Dennis and Dee Get a New Dad, Mac and Charlie Die (Part 1)) Mac is seen injecting some sort of steroid with the guidos in The Gang Goes to the Jersey Shore.

Dennis is shown with a bag of kind bud but never smoking it. (The Gang Finds a Dumpster Baby)

Dennis and Dee both smoke angel dust with the shady people they meet at the Jersey Shore to show them that they're 'cool'. The assume that they are only smoking marijuana, until they discover the smoke "burns" and that they have actually smoked PCP. (The Gang Goes to the Jersey Shore)

Frank refers to his wife Barbara Reynolds as a pill-head, but this is never shown. (A Very Sunny Christmas)

Ryan McPoyle inhales furniture polish through a sock. (Charlie Got Molested)

Bill Ponderosa spiked the milk at the wedding of his sister—Maureen Ponderosa was marrying Liam McPoyle—with bath salts. It was a dry wedding and Bill, a recovering addict, was told by his sponsor Frank Reynolds to do whatever drugs he wanted to do. The wedding guests, mostly McPoyles, then became high on the bath salts, which caused them to act like flesh-eating zombies in The Maureen Ponderosa Wedding Massacre. No members of the gang ingested the bath salt-laced milk, though Bill tried to tempt Dee Reynolds into drinking it, claiming "it will make your butthole hot."

Charlie takes a pill which he thinks makes him smarter (Flowers for Charlie)

Dennis smokes cigarettes throughout the series (Charlie Goes America All Over Everybody's Ass, The Gang Hits the Road)

Charlie huffs glue in (The Gang Tries Desperately to Win an Award)

Mac, Dennis and Dee get high off of gasoline.

Frank's girlfriend, Roxy, smokes crack throughout (Frank's Pretty Woman)

Mac and Dennis want to get crack off of Roxy in (Frank's Pretty Woman)

Drug Dealing
Bingo is Frank's shady connection that is known to trade in Oxycontin and cocaine, as well as firearms.

Mac sold marijuana in high school and attempted to sell Oxycontin to businessmen. He also sells angel dust to Dusty in exchange for her pretending to bang him. (The Gang Misses the Boat)

is in prison for selling heroin and tries to get Charlie and Mac to smuggle some to him on the inside. (Dennis and Dee Get a New Dad)

Rickety Cricket sells a lot of cocaine to homeless people, but then trades the money for two trash cans so that he can play them as drums. (The Gang Gets Whacked)