Few reports of allergic reactions, asthma, irritated sinuses, skin rashes, and skin blood vessel inflammation (vasculitis) have been reported in the available literature with the use of passion flower products. It is believed that some reactions may have been caused by impurities in combination products, not by passion flower itself.
Passion flower is generally considered to be a safe herb with few reported serious side effects. In cases of side effects, the products being used have rarely been tested for contamination, which may have been the cause. Cyanide poisoning has been associated with passiflora fruit, but this has not been proven in human studies.
Rapid heart rhythm, nausea, and vomiting have been reported. Side effects may also include drowsiness/sedation and mental slowing. Patients should use caution if driving or operating heavy machinery.
Passion flower may theoretically increase the risk of bleeding and affect blood tests that measure blood clotting (international normalized ratio or "INR").
There is a case report of liver failure and death of a patient taking a preparation of passion flower with kava. Use cautiously with any kava-containing products, as kava has been associated with liver damage. It has been suggested that the cause of the liver damage is less likely related to the presence of passion flower.
There is not enough scientific evidence to recommend the safe use of passion flower in any dose during pregnancy or breastfeeding. During the 1930s, animal studies found uterine stimulant action in components of Passiflora.
Many tinctures contain high levels of alcohol and should be avoided during pregnancy.
Certain substances (harmala alkaloids) with monoamine oxidase inhibitory (MAOI) action have been found in small amounts in some species of Passiflora. Although levels of these substances may be too low to cause noticeable effects, passion flower may theoretically increase the effects of MAOI drugs, such asisocarboxazid (Marplan®), phenelzine (Nardil®), and tranylcypromine (Parnate®). Increased sedation or low blood pressure could also result from taking passion flower with tricyclic antidepressants, such as amitriptyline (Elavil®), and selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine (Prozac®).
Based on animal research, use of passion flower with alcohol or other sedatives may increase the amount of drowsiness caused by some drugs. Examples include benzodiazepines, such as lorazepam (Ativan®) or diazepam (Valium®); barbiturates, such as phenobarbital; narcotics, such as codeine; some antidepressants; and alcohol. Caution is advised while driving or operating machinery.
In theory, passion flower may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogel (Plavix®), and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
Passion flower may also interact with anti-anxiety drugs, antibiotics, anticonvulsants, antifungals, antihistamines, anti-cancer drugs, antispasmodics, antitussives, caffeine, CNS depressants, drugs broken down by the liver, flumazenil, naloxone, and other neurologic agents.
Certain substances (harmala alkaloids) with monoamine oxidase inhibitory (MAOI) action have been found in small amounts in some species of Passiflora. Although levels of these substances may be too low to cause noticeable effects, in theory, use of passion flower with herbs or supplements with MAOI activity may cause additive effects. Kava (Piper methysticum) is believed to have weak monoamine oxidase inhibitor effects and may thus interact with passion flower. In addition, tricyclic antidepressants or selective serotonin reuptake inhibitors may lead to increased sedation or low blood pressure when taken with passion flower.
Based on animal research, use of passion flower may increase the amount of drowsiness caused by some herbs or supplements, such as valerian and kava.
Passion flower may have additive effects when taken with herbs or supplements that increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of ginkgo (Ginkgo biloba), and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
When taken with caffeine or herbs containing caffeine or caffeine-like compounds, passion flower may increase blood pressure.
Passion flower contains lycopene and may have additive effects when taken with lycopene supplements.
Passion flower may also interact with herbs or supplements taken for pain, anxiety, seizures, fungal infections, bacterial infections, or cancer. In addition, interactions with antihistamines, antispasmodics, antitussives, CNS depressants, herbs and supplements broken down by the liver, and other neurologic agents are possible.