What are The Side Effects of L-Theanine?


L-Theanine is a non-dietary amino acid found in black tea and green tea. It’s also available in supplement form to treat anxiety and insomnia. A UK study showed it improves mood, memory, and cognitive function.   

L-Theanine molecules are small enough to pass through the blood-brain barrier in half-an-hour. It restores emotional balance, promotes better sleep, induces thermogenesis (fat-burning) to encourage weight loss, reduces stress and cleanses the liver.

So what’s the catch? Any supplement with so many good qualities has to have a dark side.  Well, not really. Let’s take a look at the minimal side effects of theanine.

L-Theanine Side Effects Mayo Clinic

Although L-Theanine is used as a natural treatment for many health issues, the predominant benefits are as a nootropic (cognitive enhancer) and a gentle, natural supplement that reduces anxiety.

The Mayo Clinic recommends you talk with your doctor if you’re considering taking a supplement for anxiety. L-Theanine is considered safe for most adults (and children) with anxiety, but like other supplements, it may interfere with certain prescription medications.

If you are taking prescription anti-depressants or anti-anxiety medication, don’t take an L-theanine supplement in addition to your medicine (or switch to an L-theanine supplement) until getting the all-clear from your doctor.  

L- Theanine Side Effects Serotonin

L-theanine may decrease serotonin in the body. Serotonin is one of four neurotransmitters that carry messages along the nerves, and it’s responsible for balancing mood, along with Dopamine, GABA, and Norepinephrine.

If you’re prone to depression, it’s important to avoid any supplement, food or drink that lowers your serotonin level. While small amounts of L-theanine won’t affect most users, a dosage of 1200 mg or more a day may reduce serotonin, causing side effects, including brain fog, depression, and low energy.  Every individual is different, and you may experience reduced serotonin after taking a regular dosage of an L-theanine supplement when another person would be unaffected.  

Side Effects of L-Theanine Supplements

Serious L-theanine side effects are practically non-existent, though there are occasional minor ones. Dizziness, nausea, and headaches are the only common side effects evident in clinical studies of L-theanine.   

If you’re using Sudafed, (pseudoephedrine), epinephrine or other stimulant drugs, L-theanine may decrease the drug’s effectiveness. In one isolated case, a 38-year old woman developed blood clots in small blood vessels after drinking L-theanine rich green tea.

L- Theanine supplements may interfere with response time in some individuals. This is due to an increase in the neurotransmitter GABA L-Theanine relaxes you but doesn’t have the sedation qualities to make you drowsy. This may be a good thing if you’re highly anxious, but it may be a side effect if you’re already a laid-back type (or if you have low serotonin levels). <