St. John's wort is a herb that has long been thought to have medicinal qualities, especially for the treatment of depression.

It also appears to have antibacterial properties and may act as an antiviral agent.

Also known as Perforate St. John's wart, Tipton's Weed or Klamath weed, St. John's wort comes from a flowering plant called Hypericum perforatum. It is available in teas, tablets, capsules, and as a topical treatment.

The plant contains the active chemical hypericin, and this may be what gives the herb most of its efficacy. Other ingredients such as hyperforin and flavonoids may play a role.

St. John's Wort can clash dangerously with some prescription drugs, so care must be taken with its use, and any use should be first discussed with a health care provider.

It can also lead to increased photosensitivity, or sun sensitivity, stomach upset and allergic reactions.

Fast facts about St. John's wort

  • St. John's wort is named after St. John the Baptist, as the plant is in full bloom on 24th June, St. John's feast day.
  • The herb is used in alternative medicine to treat depression, anxiety, and attention deficit hyperactivity disorder (ADHD).
  • It can be taken in the form of tablets, tinctures, or as an infusion, using teabags.
  • St. John's wort has not been approved by the Food and Drug Administration (FDA) for over-the-counter (OTC) or prescription use in the United States (U.S.).

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St John's wort is a herb with antidepressant and potentially antiviral qualities.

St. John's Wort is named after St. John the Baptist, whose feast day (24th June) occurs when the plant is in full bloom.

Red spots are said to appear on the plant's leaves on August 29th in the northern hemisphere, traditionally the anniversary of the death of St. John the Baptist. The red spots are said to represent the blood spilled when St. John was beheaded.

Some say the herb was used to treat the wounded in the crusades by the Knights of St. John.

How it works is unclear, but its action may be similar to that of a selective serotonin reuptake inhibitor (SSRI) such as fluoxetine, or Prozac, in increasing the availability of the brain chemicals dopamine, serotonin, and norepinephrine.

St. John's wort has been used for hundreds of years in folk medicine, especially for healing wounds. It was used for "driving out the inner devil" in medieval times. Paracelsus, a 16th-century philosopher, recommended the herb for hallucinations and "dragons" and healing wounds.

In 1959 and 1971 St. John's wort's antibacterial properties were scientifically reported. Its antibacterial substance, hyperforin, was extracted and analyzed.

Nowadays, St. John's wort is widely used in Europe, especially Germany, as an herbal treatment for depression. Its therapeutic use has grown elsewhere in the world in the last 20 years.

In the United States (U.S.), the Food and Drug Administration (FDA) has not approved it either as an over-the-counter (OTC) or prescription drug to treat depression.

A 2016 review of studies concluded that St. John's wort is better than a placebo in treating mild or moderate depression. Researchers cautioned, however, that the evidence was flawed by a lack of research into the use of the therapy for severe depression and poor reporting of adverse events.

However, not all research was consistently reliable.

In most countries, St. John's wort is available OTC, but in some countries, for example, Ireland, a prescription is required.

Most people take the herb either in tablet or capsule form, but it is also available in teabags. For topical application, it is used in tinctures, a medicinal extract in a solution of alcohol.

St. John's wort has been tested a number of conditions, with varying results.

Depressive disorder: For the treatment of mild-to-moderate major depression, short-term studies, lasting up to 12 weeks, indicate that the herb is more effective than a placebo and as equally effective as tricyclic antidepressants TCAs in treating depression.

Studies comparing St. John's wort with selective serotonin reuptake inhibitors (SSRIs), such as Prozac (fluoxetine) or Zoloft (sertraline), are more limited, but there is some evidence that the herb may be as effective as these drugs and with fewer side effects.

There is not enough evidence to support its use in children.

Attention deficit hyperactivity disorder (ADHD): One small study has suggested that St. John's wort might be "slightly effective" in treating ADHD, but others have found that it did not help.

There are some concerns that it may worsen symptoms.

Anxiety disorder: There is not enough evidence to say that St. John's wort is effective against anxiety disorder, and it may make symptoms worse.

Atopic dermatitis: A study of the effectiveness of hypericum cream has suggested that mild to moderate atopic dermatitis may respond positively to topical treatment.

Somatoform disorders: Some people have physical symptoms that cannot be linked to an organic disease. St. John's wort may be useful in treating some of these, but more evidence is needed.

HIV: Some animal studies have suggested that St. John's wort may have antiviral effects, but one human trial did not support this.

The use of St. John's wort for HIV or AIDS is not recommended, because of the risk of drug interactions.

Research has also looked at the use of St. John's wort for:

Further evidence is needed to confirm its effectiveness.

The usual dose in capsule or dry tablet form, is 300 milligrams (mg) three times a day, with meals. This is for adults. It is not recommended for children.

If side effects do occur, they may include:

  • anxiety
  • dizziness
  • dry mouth
  • headache
  • light sensitivity
  • restlessness
  • sedation
  • sexual dysfunction
  • skin reactions
  • stomach upset
  • tiredness or fatigue

It may take 3 to 6 weeks to experience any benefit. Stopping the use of St. John's wort should be done gradually, to prevent side effects.

A person with a diagnosis of depression should not use St. John's wort as an alternative to therapies recommended by a doctor. If the herb is not effective, the depression may worsen.

Patients should not take St. John's wort if they are taking the following medications, as its use may make them less effective:

  • Anticonvulsants
  • Cyclosporine
  • Digoxin
  • Oral contraceptives
  • Some anti-HIV drugs
  • Theophylline
  • Warfarin

St. John's wort may increase the effect of SSRI antidepressants. This can lead to a hazardous increase in serotonin in the body.

Symptoms include:

  • tremor
  • diarrhea
  • confusion
  • muscle stiffness
  • low body temperature

It can be fatal.

In some cases, St. John's wort can trigger psychosis. People with bipolar disorder or major depression should not use it, as it may result in a mania.

It can also add to the effect of triptan drugs used for migraine, such as sumatriptan.

It is not yet clear whether St. John's wort is safe to use during pregnancy or while breastfeeding.

Patients should always discuss with their doctor first before taking St. John's wort or other supplements or alternative therapies, especially if they are already taking medications.

Supplements and herbal remedies are made of chemicals, just as conventional drugs are.

Research published in 2015 suggested that as St John's Wort has a similar profile to fluoxetine, it can also produce the same adverse reactions. Serious adverse effects could occur if the two drugs are taken together.