If you’ve been prescribed tamoxifen (sold as Soltamox), you may wonder if there’s a specific time of day you should take it. Sometimes, the time of day you take a medication can affect how well that medication works and your risk of side effects. While this is the case for some medications, there isn’t enough research to say whether taking tamoxifen at a specific time of day will impact how well it works.

There are still some factors to think about when deciding the right time to take tamoxifen. This article will review those factors and general drug information to help you and your doctor figure out the best time of day to take your tamoxifen as part of your breast cancer treatment plan.

What Is Tamoxifen?

Tamoxifen is a hormonal therapy used to treat hormone receptor (HR)-positive breast cancer. You may take tamoxifen either as a treatment for breast cancer or as prevention if you have a high risk of developing it. You can take tamoxifen if you have or haven’t been through menopause. For treating early breast cancer, most people take it for five years, though some people continue taking it for up to 10 years. People who take it to reduce their risk of breast cancer also usually do so for about five years.

Tamoxifen helps reduce the risk of new or recurrent breast cancer by blocking the effect of estrogen on breast cancer cells. In HR-positive breast cancer, estrogen can encourage growth of cancer cells. By blocking estrogen, tamoxifen can slow or stop the growth signals estrogen sends.

How Should You Take Tamoxifen?

You should take tamoxifen exactly as your doctor instructs you to take it — don’t take more or less than prescribed.

Tamoxifen comes as a tablet or a solution that you take orally. If you take the tablet, you should swallow it whole — don’t break, crush, or chew it. If you take the solution, make sure to use the provided dosing cup.

Tamoxifen is usually taken once or twice a day, at the same time each day. A dose of 20 milligrams is usually taken once a day. A 40-milligram daily dose is often divided into two doses, with the first taken in the morning and the second in the evening.

You can take tamoxifen with or without food. However, you should avoid grapefruit and grapefruit juice while you’re taking the drug. Grapefruits contain a chemical that can increase your risk of side effects from tamoxifen.

The time of day you take tamoxifen doesn’t have a significant impact on how well it works. A small study looked at the effects of taking the drug at different times of the day. Even though there were some small differences, the researchers concluded that time of day wouldn’t impact how well tamoxifen worked.

Currently, there isn’t any clinical research studying the best time of day to take tamoxifen. However, there is an ongoing clinical trial — expected to be completed in 2023 — evaluating the best time of day to take endocrine therapy (hormone therapy), including tamoxifen.

What Are the Possible Side Effects of Tamoxifen?

The type and severity of side effects of tamoxifen are different for everyone. The most common side effects include:

• Hot flashes (also known as hot flushes, sweats)
• Fatigue or excessive tiredness
• Vaginal discharge
• Vaginal bleeding
• Hair thinning
• Dry skin
• Depression
• Mood swings
• Nausea
• Constipation
• Fluid retention

You may experience a few or none of these side effects, but you likely won’t get all of them.

There isn’t any research into whether taking tamoxifen at different times of the day might affect the side effects you experience.

How To Choose When To Take Tamoxifen

The time of day you take tamoxifen is a personal decision. With this medication, you don’t need to consider a specific time of day or meal times, but there are some other factors that may help you choose what time of day works better for you.

Make sure to talk to your oncologist or other health care provider before changing the time of day you take tamoxifen. It’s important to take your medication exactly as instructed.

Consider Your Other Medications

If you are premenopausal, you may take tamoxifen and other cancer drugs as a way to stop your ovaries from working and producing estrogen — known as ovarian suppression. You might also take medications, vitamins, or supplements for other medical conditions.

When thinking about what time to take tamoxifen, ask yourself if any of your other medications need to be taken:

• At a specific time of day?
• With food?
• On an empty stomach?
• Separate from other medications?

Since tamoxifen doesn’t have strict rules about when it should be taken, you can plan when to take it around when you take other medications.

Look at Your Schedule

The best time to take tamoxifen is when you remember to take it. You can incorporate your tamoxifen into your schedule whenever it works best for you.

MyBCTeam members have shared what works best for them. One member shared, “I take it right before bed. Any other time, and I think I might forget a dose here and there. I keep the bottle right by my bed and take a glass of water with me as part of my nighttime routine.”

Another member who takes their tamoxifen in the morning shared, “I have a system, I was put on Caltrate 600+D for bones, potassium, and magnesium for muscle cramping and tamoxifen. I set the tamoxifen on top of my Caltrate bottle on my bathroom sink, and first thing in the morning, I take everything so I don’t forget.”

Observe Your Side Effects

There isn’t enough information to say that people may have more or fewer side effects if they take tamoxifen at a specific time of day. It’s important to discuss any new, lingering, or severe side effects with your health care provider. Changing the time of day you take tamoxifen may be an option to help manage some of tamoxifen’s side effects.

In one study, women reported that changing the time they took tamoxifen affected the timing and severity of hot flashes. However, this finding needs to be further investigated.

MyBCTeam members have shared how the time of day they take their medications can affect their side effects. One member started off taking it in the mornings but then switched to nighttime. They shared, “I started taking 20 milligrams in the morning, but it made me nauseous and I had trouble eating. I lost about 5 pounds that I didn’t really need to lose, so I switched to taking it at night.”

Another member started taking it at night, but switched to the morning saying, “I started taking it at night but then switched to morning. I haven’t experienced many symptoms — only once in a while, I get angry for no reason.”

Another member who takes it in the morning shared, “I sleep better if I take it in the morning.”

Some people don’t notice a difference in side effects whether they take it in the morning or evening. A MyBCTeam member commented, “To tell you the truth, I’ve taken it both morning and evening and do not notice any difference. I was so worried about the side effects before taking it. You never know how your body will react until you start.”

Talk With Others Who Understand

On MyBCTeam — the social network for people with breast cancer and their loved ones — more than 64,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

What time of day do you take tamoxifen? Does tamoxifen timing make a difference in your side effects? Share your experiences in the comments below, or start a conversation by posting on your Activities page.