I'm getting pilonidal sinus excision and I was wondering if smoking marijuana would affect the healing?

It may. Are you overweight? Weed often stimulates appetite and would keep you from losing weight that you may need to. Even if you are not overweight, using weed, despite its being legal in many localities, is not good for your health, especially your brain and mental health. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex.