Chemicals of addiction - introduction

What chemicals have been known to result in addiction?  Why is it so hard to quit?  

Chemicals of addiction - Sugar

The effects of sugar on the nervous system and how sugar can be addictive.

Chemicals of addiction - Caffeine

The effects of caffeine on the nervous system and how caffeine can be addictive.

Chemicals of addiction - Alcohol

Effects of alcohol on the nervous system.

Chemicals of addiction - Nicotine

The effects of nicotine on the nervous system and why it is so addictive.

Chemicals of addiction - Marijuana

The effects of marijuana on the nervous system.

Chemicals of addiction - Opioids

Effects of opioids on the nervous system and why they are addictive.

Chemicals of addiction - Ecstasy

What are the effects of ecstasy on the nervous system and is it addictive.

Chemicals of addiction - Cocaine

What are the effects of cocaine on the nervous system and why is it addictive.

Chemicals of addiction - Methamphetamine

What are the effects of methamphetamine on the nervous system and why is it so addictive.