Harris roach tablets kill cockroaches, but they work slowly and only on roaches that eat them

Harris roach tablets are a boric acid bait product designed to poison cockroaches when they consume the tablet material. The tablets themselves do not kill roaches on contact. Instead, a roach must crawl across the tablet, pick up the powder on its body and legs, return to its nest or hiding spot, and then ingest the poison during grooming. This means you will not see dead roaches when ready — the process typically takes three to seven days after a roach has eaten enough of the bait.

The tablets work best in kitchens, bathrooms, and other areas where roaches actively forage for food and water. They are most effective against German cockroaches, the species most common in homes. However, they are less reliable against larger roaches like American cockroaches, which may avoid the bait entirely or require a much larger dose.

Harris tablets contain boric acid, which is toxic to insects but poses a risk to children and pets if ingested. This is why placement matters: the tablets must go in areas roaches frequent but where people and animals cannot reach them — behind appliances, under sinks, inside cabinets, or along baseboards in low-traffic zones.

Key Takeaways

  • Harris roach tablets kill by poisoning, not contact, so roaches must eat the bait for it to work.
  • Results take three to seven days because the roach must groom itself and ingest the powder it picked up.
  • The tablets work best in enclosed spaces like under sinks and behind appliances where roaches hide and forage.
  • Boric acid is toxic to humans and pets, so tablets must be placed where children and animals cannot access them.
  • A single process rarely solves a roach problem — most infestations require repeated placement and often a second method alongside the tablets.

Why roaches must eat the bait for it to work

Boric acid, the active ingredient in Harris tablets, is a stomach poison. It does not kill on skin contact the way some insecticides do. A roach walking across a tablet picks up fine powder on its legs and body, but nothing happens until the roach grooms itself — a behavior roaches do constantly — and swallows the powder. Once ingested, boric acid damages the roach's digestive system and nervous system, leading to death.

This delay is actually an advantage in one way: the roach has time to return to its nest or hiding spot before it dies. There, other roaches may feed on the dead roach's body, ingesting boric acid themselves. This secondary poisoning can extend the effect beyond the roaches that directly ate the bait. However, it also means you may not see results for a week or more, which frustrates homeowners expecting faster action.

Not every roach in your home will find or eat the tablets. Roaches that avoid the baited areas, or that prefer other food sources, will not be affected. This is why tablets alone rarely eliminate an entire infestation.

Where to place tablets for the best results

Harris tablets work only where roaches travel and forage. Place them along the routes roaches use to move between their hiding spots and food sources. Common placement zones include the space behind and under the refrigerator, under the kitchen sink, inside cabinet corners, along baseboards in the kitchen and bathroom, and behind the stove or dishwasher.

Roaches are drawn to moisture and food residue, so bathrooms and kitchens are priority areas. Place tablets in the corners of cabinets, under the sink where pipes enter the wall, and along the floor where the wall meets the baseboard. In bathrooms, focus on under the sink, around the toilet base, and behind the toilet tank.

Keep tablets away from areas where children play, where pets sleep, or where food is prepared. Do not place them on countertops or in open spaces. Roaches are nocturnal and prefer tight, dark spaces — tablets in the open are less likely to be found and more likely to be discovered by a child or pet.

How long it takes to see results

Most roaches that consume Harris tablets die within three to seven days. However, you may not see the dead roaches because they often die in hidden spaces — inside walls, under appliances, or in other areas you cannot access. The first sign of success is usually a reduction in roach sightings over one to two weeks, not a pile of dead roaches.

If you see no change after two weeks, the tablets may not be reaching the roaches in your home. This can happen if the infestation is large, if roaches are avoiding the baited areas, or if they are finding abundant food elsewhere and have no reason to eat the bait. In these cases, moving the tablets to new locations or combining them with another method — such as gel baits or a professional treatment — becomes necessary.

Limitations of tablets alone

Harris roach tablets are a low-cost option, but they have real limitations. They work slowly, they require roaches to actively consume the bait, and they do not address the conditions that attracted roaches in the first place. A home with standing water, food crumbs, or clutter will continue to attract roaches even after the tablets kill the current population.

Large infestations often require more than tablets. Gel baits, which roaches find more attractive and consume more readily, may work faster. Insecticide sprays kill on contact and can reach roaches in areas tablets cannot. Professional pest control services use a combination of methods and can treat wall voids and other spaces a homeowner cannot access.

Tablets are most effective as part of a broader strategy: clean up food and water sources, seal cracks and gaps where roaches enter, use tablets in high-traffic areas, and monitor for activity. If roaches persist after two to three weeks, or if the infestation is severe, calling a pest control professional is the more reliable choice.

Safety considerations with boric acid

Boric acid is toxic if swallowed by humans or pets. Harris tablets are designed to be placed in areas roaches access but people and animals do not. However, accidents happen. A child crawling behind a cabinet or a pet chewing in a dark corner can find a tablet.

If someone in your household ingests boric acid, call Poison Control at 1-800-222-1222 when ready. Symptoms of boric acid poisoning include nausea, vomiting, diarrhea, and in severe cases, seizures. Do not wait to see if symptoms develop — call right away with the product name and the amount ingested.

Store unused tablets in their original container, out of reach of children and pets. Wash your hands after placing tablets. Do not use tablets in homes with very young children or in areas where pets spend unsupervised time.

Comparing tablets to other roach control methods

Harris tablets are one option among several. Gel baits (like Combat or Advion) are often more attractive to roaches and work faster — roaches consume them more readily than powder tablets. Roach traps do not kill roaches but show you where they are traveling and how severe the problem is. Insecticide sprays kill on contact but require you to spray directly on roaches or in their hiding spots, and the chemicals dissipate quickly.

For a mild infestation caught early, tablets or gel baits may be enough. For a moderate to severe infestation, combining tablets with gel baits and traps, plus cleaning and sealing, gives better results. For a very large infestation or one that persists despite your efforts, professional pest control is the most effective route. A pest control technician can treat areas you cannot reach, use stronger materials, and monitor the problem over time.

Frequently Asked Questions

Will Harris roach tablets kill all the roaches in my house?

No. Tablets kill roaches that find and eat them, but roaches that avoid the baited areas or that are hiding in wall voids or other inaccessible spaces may not be affected. Most infestations require multiple methods or professional treatment to fully resolve.

Can I use Harris tablets in my kitchen near food?

No. Tablets must be placed where roaches forage but where food preparation does not happen. Use them under the sink, behind appliances, and along baseboards — not on countertops or in cabinets where you store food or dishes.

How many tablets should I use?

Follow the label instructions on the Harris product you purchase. Generally, place tablets every few feet along roach travel routes. Start with the recommended amount, monitor for activity over two weeks, and add more tablets to new locations if roaches persist.

What should I do if the tablets are not working after two weeks?

Move the tablets to different locations, as roaches may be avoiding the original spots. Consider adding gel baits, which roaches often prefer. If activity continues after three weeks, contact a pest control professional — the infestation may be too large or too well-established for tablets alone.

Is it safe to use Harris tablets if I have a dog or cat?

Tablets can be used safely if placed where your pet cannot reach them — behind appliances, inside cabinets, or in areas your pet does not enter. If your pet has access to most of your home, tablets are not a safe choice. Gel baits in tamper-resistant stations are a safer alternative.