Mild

• Mild side effects from chlorella that have been reported include nausea, bloating and stomach upsets, although these usually disappear after a short time of use. Some people using chlorella have developed a sensitivity to sunlight.
  
  

Allergic Reaction

• Chlorella causes an allergic reaction in some users, which manifests as breathing difficulties, a tightness in the throat or chest, chest pains, skin hives, rash, itching or swollen skin. If you experience any of these allergic symptoms, stop taking chlorella immediately and consult your doctor
  
  

Malabsorption

• Chlorella's tough, cellulose cell wall is hard to digest. As a result, people who suffer from cellulase enzyme insufficiency cannot tolerate intake of chlorella because they lack the enzyme necessary to digest it. To use this supplement, they will have to take it in conjunction with a digestive enzyme supplement that contains cellulase to facilitate the digestion of chlorella. This cellulase digestive supplement is available in most health food stores.
  
  

Mercury

• There is anecdotal evidence that chlorella is relatively high in mercury content, at levels that are higher than what is considered safe. Intake of high levels of mercury can result in tingling sensations in the toes, fingers and lips, as well as headaches, fatigue, irritability, muscle weakness and loss of concentration. There are, however, no clinical studies to support this.
  
  

Uric Acid

• Chlorella has been found to raise the uric levels in the blood. This tends to exacerbate gout, which is a rheumatic condition in which uric acid crystals form in the joints. High uric levels also present a risk factor for heart disease.
  
  

Considerations

• Since chlorella is sold as a supplement rather than a drug, there is no requirement for extensive clinical studies on its side effects or interactions. For this reason, full studies on harmful side effects are not readily available, and detailed information on ill effects and interactions are incomplete.
  
  

Warning

• With such little research conducted on this popular supplement, pregnant women should err on the side of caution and avoid taking it. This is even more important because of the potentially high mercury content level.