SAM-e

SAM-e, pronounced "sammy", is short for S-adenosyl-L-methionine. It's a chemical that's found naturally in the human body and is believed to increase levels of neurotransmitters serotonin and dopamine.

Several studies have found SAM-e is more effective than placebo.

In North America, SAM-e is available as an over-the-counter supplement in health food stores, drug stores, and online. It should be enteric-coated for maximum absorption. 

Although it's one of the more expensive supplements, it remains popular as a remedy for depression and osteoarthritis.

Side effects can include nausea and constipation.