Gamma-aminobutyric acid (GABA) is a dietary supplement that is used for a variety of mood-related conditions, including anxiety, depression and panic disorder. It also is used to boost exercise tolerance and muscle growth. Reported GABA side effects range from increased blood pressure and heart rate to unusual sensations around the face, wheezing, faster breathing, drowsiness and a sense of calm that sometimes is referred to as an emotional disconnection. Other symptoms reported less often include mild nausea and the face becoming flush.

Although some studies of bodybuilders show no GABA side effects even at high doses, average people have reported GABA side effects at much lower doses. This might be because of GABA’s varying effects on people of differing body types, nutritional status and athletic conditioning. In addition, the supplement might not be suitable for people who have medical conditions such as asthma and high blood pressure, because specific GABA side effects such as faster breathing and increased blood pressure can exacerbate the symptoms that come with these diseases.

GABA can be swallowed as capsules or absorbed under the tongue but is contraindicated for pregnant women, because GABA's effects on pregnancy are not understood. There is little scientific information available regarding GABA dosing, and physician guidance might be needed. The most common anecdotal GABA side effects, increased heart rate and breathing and tingling sensations around the face, typically are temporary for those reporting them.

Although GABA normally exists in the body as both an amino acid and a neurotransmitter, lower levels in the blood have been found in people who have bipolar disorder or depression. In addition, women whose menstrual changes lead to depression have lower levels of GABA in their blood. GABA also might decline with age in both men and women.

There is limited scientific research on supplemental GABA's benefits. Some studies have shown that supplementing with GABA reduces over-stimulation in the brain and induces a relaxed state. This has led to its use for depression and anxiety as well as insomnia. GABA also is believed to stimulate the area of the pituitary gland that generates human growth hormone, which in turn can help increase muscle mass. This make GABA appealing to bodybuilders.

Some scientists, however, believe that ingested GABA cannot penetrate the blood-brain barrier, which prevents the supplement from reaching and benefiting brain cells or affecting the pituitary gland. Despite this theory, anecdotal evidence from people taking GABA suggests it works for some. Those taking it for anxiety and sleeplessness report the most benefit.