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Making a weekly shopping trip to Costco helps me save more money on groceries and household essentials, like cleaning supplies and toilet paper. By purchasing these items in bulk, I pay less on a per-ounce or per-unit basis compared to my regular supermarket in town.

But you need to be careful with certain items when buying in bulk. Despite the potential savings, I’d suggest purchasing these three things at your regular supermarket instead of Costco.

1. Over-the-counter medication

At Costco.com, 1,000 ibuprofen tablets cost $12.99, or $0.01 per tablet. And Costco’s in-store prices are pretty much always lower than its online prices, which means that buying 1,000 pills from your local store could save you even more money. At my local supermarket, a 100-pill supply of Ibuprofen costs $4.49, so I’m paying $0.04 per pill.

But I don’t use ibuprofen daily, and those pills only last for so long before they lose their potency. So if I spend $12.99 on 1,000 pills, I’m likely to throw most of them out. If I spend $4.49 on 100 pills and that quantity lasts me the year, that’s the better deal for me.

I’d encourage you to think carefully about your medication usage. You may want to avoid bulk purchases of over-the-counter medications you tend to use sparingly.

2. Flour

I like to bake, so I find myself replenishing the five-pound bags I buy at the supermarket pretty often. But there’s a reason I refuse to buy 20 pound bags of flour from Costco. Despite the potential savings, I’m opening the door to spoilage and a huge hassle.

Flour can last a while once it’s opened if you store it in an airtight container. But I only have so many of those. It’s better for me to just buy flour in five-pound increments rather than figure out how to keep four times that amount fresh enough to use for months.

Also, Costco doesn’t always have the best prices on flour. Right now, you’re looking at paying $1 per pound if you buy your flour online. But my local supermarket has flour for about $0.72 per pound. And even though that per-pound price at Costco is likely to be cheaper in stores than online, it’s probably not going to beat $0.72 per pound by much. So why deal with the extra hassle?

Of course, if you bake multiple batches of cookies or cakes a week or run a baking business out of your home, then buy your flour from Costco if you find that the price there is better. But otherwise, you should probably buy it from your regular supermarket.

3. Food items you’ve never tried before

If your family eats eggs almost every day or goes through cherry tomatoes like nobody’s business, then it probably pays to scoop up these items in bulk at Costco. But generally speaking, you shouldn’t buy items in bulk you’ve never tried before.

You might think chocolate-covered blueberries sound like a delicious snack only to realize you’re not a fan. (This is an actual item Costco sells, and while I love it, my husband insists it’s terrible.) A better bet is to try a smaller amount at your regular supermarket first, then purchase a bulk supply from Costco if you end up loving whatever the new product is that you’re trying.

Be strategic with your bulk purchases

Costco’s prices are often hard to beat, so it can be tempting to buy a host of products there. But these three items are a big exception.

The good news is that with the right approach, you can save plenty of money on your supermarket shopping. One way to lower your costs is to be on the hunt for coupons. Another is to use the right credit card at checkout. Click here for a list of the best credit cards to use at Costco.

And don’t forget to sign up for a shopper’s card at your local supermarket for added savings and incentive programs. Right now, for example, my local store is giving out free turkeys to customers who spend $400 between late October and late November. You may find similar programs available at your neighborhood supermarket throughout the year, so it pays to keep tabs on the perks your local grocery store offers.

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The Ascent does not cover all offers on the market. Editorial content from The Ascent is separate from The Motley Fool editorial content and is created by a different analyst team.Maurie Backman has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Costco Wholesale. The Motley Fool has a disclosure policy.