Go For GLA by Go For GLA If you've ruled out other causes of hair loss, such as stress, overuse of hair-care products, and certain medications and diseases such as hypothyroidism, consider supplementing with evening primrose oil. It's a good source of gamma-linolenic acid,an essential fatty acid that's needed for hair growth and is hard to get from your diet. Experts recommend taking 500 milligrams twice a day; expect to wait eight weeks to see results.