Birch

Medication/Health Condition: Contraindicated: Aspirin (oral use), Anticoagulants (such as Warfarin and Heparin, all routes), ADD/ADHD if have salicylate sensitivity (topical and oral use), Childbirth and Major Surgery (all routes one week before and after), Epilepsy (limit 5-6 drops/day orally), GERD (oral use), Peptic Ulcer (all routes), Hemophilia and other bleeding disorders (all routes) 

Methyl salicylate (the key constituent of Sweet Birch and Wintergreen) inhibits platelet aggregation and exacerbates blood thinning. 

Robert Tisserand, aromatherapist and author of Essential Oil Safety, wrote about Wintergreen, but we include this information here because Birch is almost identical, chemically speaking, to Wintergreen: "In Europe, the ADI (‘acceptable daily intake’) for methyl salicylate is 0.5 mg/kg/day, which equates to about 1 drop of Wintergreen oil per adult per day. ADIs are primarily intended to cover the food industry. This regulation does not apply outside of Europe."

"There is no difference between Wintergreen oil toxicity and methyl salicylate toxicity. Methyl salicylate is one of the ingredients in Listerine, so many people use it daily in a mouthwash, and very small amounts may be ingested. As always, toxicity is in relation to dose. I would suggest that Wintergreen oil is not one that should be taken orally as a medicine, unless under the supervision of a doctor or herbalist. There have been many fatalities from (accidental) overdose, and there are a number of toxicity issues – it’s fetotoxic, there are several reasons why it could be problematic in children, it’s extremely blood-thinning, and should be avoided by people with GERD. So it’s not just a question of how much is toxic – it’s also about individual sensitivity. It should absolutely never be taken during pregnancy. Like all salicylates, it causes fetal malformations. Even externally, it can cause problems."

Dermal Use: Maximum level 2.5%
"Wintergreen oil has some wonderful properties, but I would not like to see it used at more than 5%. No one has died from dermal [topical] application, but there have been at least three reported cases of people taking blood-thinning medication who broke out in internal bruising when they applied methyl salicylate-containing products to their skin. It enhances the blood thinning action of the drug, and blood leaks out of the blood vessels." 

"Methyl salicylate is good for some people, not for others. A blanket contraindication is not necessary, but it is best avoided in pregnancy – all salicylates are teratogenic in sufficient amount, including methyl salicylate and aspirin (acetyl salicylic acid). Methyl salicylate must be absolutely avoided by anyone taking blood-thinning drugs, as it increases the action of the drug, and this causes blood to leak into tissues and internal bruising occurs. Knowing a lethal dose tells you very little about what (1) a therapeutic dose would be or (2) a safe dose would be, but it does tell you what dose not to use! Therapeutic dose is good to know of course, and this varies between essential oil and also between purpose. Wintergreen oil has some wonderful properties, but I would not like to see it used at more than 5%."

Avoid contact with the eyes and other sensitive areas. Essential oils are both lipophilic and hydrophobic. Lipophilic means they are attracted to fat— like the membranes of your eyes and skin. They are also hydrophobic, meaning they do not like water. Flushing with water will only send the essential oil back to the eye's membranes. Applying a carrier oil will create another fat for the essential oil to be attracted to other than the membranes of the eyes or skin. Tisserand suggests: "With essential oils, fatty oil has been suggested as an appropriate first aid treatment, though the advantage of saline [eyewash] is that the eyes can be continually flushed, and this is less easy with fatty oil." We’ve not known this to cause permanent injury or long-term discomfort, but if you feel concerned, please call your health care provider.