In the photo above, you can see the exact Kirkland Signature sleep aid that I took every night for a week to see if it would help me through a patch of insomnia. As it’s an antihistamine, I was also curious to see if it would help with my dust mite allergy, which has been flaring up again recently.
Kirkland Signature is a private brand of Costco, and their sleep aid is widely available in the United States, both in stores and online. The main active ingredient is the antihistamine Doxylamine Succinate, which is also used in some other brands of sleep aids.
For example, another popular sleep aid – Unisom SleepTabs – has the same ingredients. Perhaps that’s why they felt the need to state on the label that it’s not made by the same company!
In this Kirkland sleep aid review, I’ll be describing my experience of taking it, which should in theory be very similar to when I tried Unisom. I’ll also discuss some of the warnings and side effects at the end.
The first night
My first impression was that the Kirkland sleep aid is, like Unisom, very small and easy to swallow.
The instructions tell you to take one tablet 30 minutes before going to bed. So I took one just as I got into bed and then read for a while. I always like to read after testing a sleep aid to see if there are obvious signs of sedation.
And since I was staying with a friend again, who has a notoriously dusty house (sorry if you’re reading this!), I wanted to see if it would stop my sniffling.
After around 30-40 minutes of reading, I did feel that my nose was less irritated. I didn’t feel any obvious drowsiness, but I turned the light off to go to sleep anyway.
I woke up around 6.5 hours later, which is a good result for me. I often wake in the night at least a couple of times, and an average good night for me normally means somewhere between six and seven hours’ sleep.
I felt a little groggy on first waking up, but it cleared up after a shower and coffee. This was again very similar to the first time I took Unisom.
The following nights
As I was expecting, the pattern for the rest of the week when taking the Kirkland sleep aid was quite similar to the Unisom – though not exactly the same, just to be clear.
One thing is for sure: it definitely helped in my eternal battle with the invisible hordes of dust mites.
As for sleep, I slept pretty well for five of the remaining six nights, despite some sporadic wakings. On the fifth night, I really didn’t feel any drowsiness and had a restless night. Maybe I slept well again the final night through tiredness. It’s impossible to say for sure.
Increasing morning grogginess
The groggy next-day effect increased throughout the week, as it has done with all the antihistamine sleep aids I’ve tried in the past. This seems inevitable if you continue taking them, which is why I rarely take them for more than a few nights at a time.
So by the fourth morning, it was taking a couple of hours to transition from what I’d put as 70% alertness on waking to 100% alert.
Still, it’s not a bad trade-off for what felt like a reasonably good night’s sleep, and distinctly better than the lack of alertness I feel after a night of endless tossing and turning.
All in all, I felt like it did its job of helping me fall sleep when I was having trouble sleeping in the previous days. The side effects were tolerable, but I wouldn’t want to push it and keep taking the sleep aid for longer.
What evidence is there that the Kirkland sleep aid works?
As with most over the counter sleep aids, the manufacturer doesn’t need to conduct clinical trials to sell it. All they need to do is adhere to the general standards in the country where supplements and ingredients of this type are concerned.
So, it’s probably more useful to see what evidence there is that the active ingredient works as a sedative. And for that, there’s no shortage of medical sites that talk about it causing drowsiness. The FDA even approved Unisom for use as a sleep aid.
A team of researchers in 2012 pointed out that it’s been an established drug for more than 50 years:
Currently, doxylamine medicinal products have been authorized for more than 50 years, with an appropriate extent of use, for symptomatic treatment of occasional insomnia, making doxylamine a drug with a well established use.
However, a team of researchers in 2015, which examined previous research studies into over the counter sleep aids, had this to say:
Currently available literature suggests that commonly used OTC sleep agents, especially antihistamines and valerian, continue to lack robust clinical evidence supporting efficacy and safety in relevant populations
This lack of evidence might also be reflected in the fact that some websites with many customer reviews have a mixture of people saying sleep aids like this one either work amazingly well or do nothing at all.
Perhaps there’s a placebo effect at work in some cases – something I’ve wondered many times in my own tests of sleep aids. Having said that, the placebo effect can be a powerful thing!
According to the patient leaflet in the box I bought, these are the ingredients:
- There’s one active ingredient – Doxylamine Succinate, 25 mg
- Dibasic calcium phosphate
- FD&C blue no. 1 aluminum lake
- Magnesium stearate
- Microcrystalline cellulose
- Sodium starch glycolate
As I mentioned earlier, these were exactly the same ingredients as Unisom SleepTabs when I bought them both.
Who shouldn’t take this sleep aid
The box came with the following warnings:
1. Speak to a doctor before use if you have:
- A breathing problem, such as asthma, emphysema or chronic bronchitis
- Difficulty urinating because of an enlarged prostate gland
2. Ask a doctor or pharmacist if:
- You are taking any other medication
3. When using this sleep aid:
- Avoid alcohol
- Only take it at bedtime
4. Stop and speak to a doctor if:
- The sleep problem continues for two weeks
5. If pregnant or breastfeeding:
- Speak to a health professional first
6. Keep out of reach of children
7. If you overdose, get medical help or call a poison center
If you’d like to check this and more safety information, you can see the Kirkland Signature factsheet on drugs.com.
Warnings for older adults and children
I’ve seen an increasing number of medical sites recommend that older adults, as well as children, avoid Doxylamine Succinate. For example, WebMD says:
Older adults may be more sensitive to the side effects of this drug, especially drowsiness, dizziness, low blood pressure, confusion, constipation, or trouble urinating. Drowsiness, dizziness, and confusion can increase the risk of falling.
If you’d like some in-depth information about the use of this type of sleep aid among older adults, there’s an interesting research study from 2017 which looks into the issue and explains why it’s a potential problem.
Healthline also has a clear article explaining why it’s not recommended to take an antihistamine for sleep every night. It explains that doxylamine succinate also has anticholinergic properties. And that research has explored how the cumulative effect of taking anticholinergic medication increased the risk of dementia and Alzheimer’s disease.
Possible side effects
Like most over the counter sleep aids, the manufacturer is not required to list every possible side effect. This is one of the issues with sleep aids sold as supplements rather than prescription drugs.
So, as with Unisom, I’ve checked medical sites like Mayo Clinic, WebMD, and others for the known possible side effects of the active ingredient. They are:
- Dry mouth, nose or throat
- Constipation or difficulty urinating
- Stomach upset
- Memory problems
- Blurred vision
- Worse coordination
- Irregular or fast heartbeat
- Ringing in the ears
- Mental or mood changes (e.g. confusion, irritability, hallucinations)
- Easy bruising/bleeding
So is it safe to take?
Many drugs can cause side effects, often with scarily long lists of possible side effects. But generally, Doxylamine Succinate is tolerated reasonably well by most people in the short term.
Having said that, I recommend asking your doctor for their opinion first, even though it’s available over the counter. They can give you the best advice based on your personal medical history and other factors such as any medication you take. If you’re an older adult, or buying it for a child, I would avoid this sleep aid.
If you decide to try it, I wouldn’t recommend taking it for more than a week or two at the most based on my own experience. And if you have any side effects, stop taking it.
Finally, try to work on your sleep problems naturally by following good sleep hygiene techniques.
Have you tried Kirkland Signature sleep aid? It’s always useful for readers to know what others think. So please feel free to share your experience in the comments below.