Generally, it is recommended by the Food and Drug Administration (FDA) that phentermine should be used short-term (usually interpreted as 'up to 12 weeks'), while following nonpharmacological approaches to weight loss such as healthy dieting and exercise. However, recommendations limiting its use for short-term treatment may be controversial. One reason given behind limiting its use to 12 weeks is drug tolerance, whereby phentermine loses its appetite-suppressing effects after the body adjusts to the drug. On the contrary, it has been shown that phentermine did not lose effectiveness in a 36-week trial.[2] Developing tolerance can usually be avoided long-term by taking phentermine 5 consecutive days, then skipping 2 days each week. Due to the risk of insomnia, it is generally recommended that the drug be taken either before breakfast or 1-2 hours after breakfast.