When Losartan Should Not Be Used (Contraindications)
There are specific situations where Losartan should not be taken:

Allergy: If you are allergic to Losartan or any of its ingredients.
Pregnancy: Especially during the second and third trimesters, as it can harm the developing fetus. If you become pregnant while taking Losartan, inform your doctor immediately to switch medications.
Kidney Artery Stenosis: If both arteries leading to your kidneys are narrowed, Losartan can worsen kidney function. If you have only one kidney and its artery is narrowed, it might still be a concern.
High Potassium Levels (Hyperkalemia): If you already have high potassium levels due to a medical condition, Losartan can further increase them, which can be harmful.
Severe Liver Failure: While mild liver problems might be manageable, severe liver failure is a contraindication.
Children: It’s generally not recommended for children under six years old.
Drug and Herb Interactions
It’s important to be aware of potential interactions:

NSAIDs: Non-steroidal anti-inflammatory drugs like ibuprofen or naproxen can increase potassium levels and may reduce the effectiveness of Losartan, potentially affecting kidney function.
Potassium-Sparing Diuretics: Medications like spironolactone or amiloride, when taken with Losartan, can significantly raise potassium levels.
Potassium Supplements: Taking potassium supplements along with Losartan can lead to dangerously high potassium levels.
Lithium: Losartan can increase lithium levels in the blood, potentially making it toxic.
ACE Inhibitors: Combining Losartan with ACE inhibitors (like enalapril) is generally not recommended due to an increased risk of side effects, including high potassium and low blood pressure.
Other Blood Pressure Medications: While often combined intentionally, always discuss combinations with your doctor.
Herbal Interactions: Some herbs can also interact with Losartan:

St. John’s Wort: May decrease Losartan’s effectiveness.
Licorice: Especially in concentrated forms, can raise blood pressure and reduce Losartan’s effectiveness.
Garlic: In large amounts, might enhance Losartan’s blood pressure-lowering effect.
Ginkgo Biloba: Evidence is mixed, but it might affect blood pressure control.
It’s always best to inform your doctor about any herbal supplements or over-the-counter medications you are taking to avoid potential problems.